High collocation of sand lance and protected top predators: Implications for conservation and management

Tammy L Silva,Gavin Fay,Hannes Baumann,Michael A Thompson,Justin J Suca,Peter Hong,David N Wiley,Joel K Llopiz,Les Kaufman

doi:10.1111/csp2.274

Abstract

AbstractSpatial relationships between predators and prey provide critical information for understanding and predicting climate‐induced shifts in ecosystem dynamics and mitigating human impacts. We used Stellwagen Bank National Marine Sanctuary as a case study to investigate spatial overlap among sand lance (Ammodytes dubius), a key forage fish species, and two protected predators: humpback whales (Megaptera novaeangliae) and great shearwaters (Ardenna gravis). We conducted 6 years (2013–2018) of standardized surveys and quantified spatial overlap using the global index of collocation. Results showed strong, consistent collocation among species across seasons and years, suggesting that humpback whales and great shearwater distributions are tightly linked to sand lance. We propose that identifying sand lance habitats may indicate areas where humpbacks and shearwaters aggregate and are particularly vulnerable to human activities. Understanding how sand lance influence predator distributions can inform species protection and sanctuary management under present and future scenarios.

Highlights

Spatial relationships between predators and prey provide important ecological insights
We focused on humpbacks and shearwaters due to their frequent occurrence and high abundance in Stellwagen Bank National Marine Sanctuary (SBNMS), their use of sand habitat and known consumption of sand lance, and their increased vulnerability to human activities in SBNMS compared with other species (Office of National Marine Sanctuaries (ONMS), 2020)
While global index of collocation (GIC) does not quantify potential predator–prey encounters, we suggest that humpbacks and shearwaters consistently aggregate on the southwest corner of Stellwagen Bank targeting sand lance as prey

Summary

| INTRODUCTION

Spatial relationships between predators and prey provide important ecological insights. The degree and scale of spatial overlap between predators and prey can indicate the potential strength of their ecological interactions (Carroll et al, 2019). Inferring predator dependence on prey species through spatial overlap studies may better inform management of prey populations (Eero et al, 2012; Koehn et al, 2020). We used Stellwagen Bank National Marine Sanctuary (SBNMS), a 2,180 km federal Marine Protected Area in the southwestern Gulf of Maine (GOM), as a case study to investigate seasonal spatial overlap between northern sand lance (Ammodytes dubius) and two protected top predators, the humpback whale (Megaptera novaeangliae) and great shearwater (Ardenna gravis; hereafter referred to as shearwaters). We focused on humpbacks and shearwaters due to their frequent occurrence and high abundance in SBNMS, their use of sand habitat and known consumption of sand lance, and their increased vulnerability to human activities in SBNMS compared with other species (Office of National Marine Sanctuaries (ONMS), 2020)

| METHODS

| RESULTS

| DISCUSSION